抄録
The mechanical properties and deformation behaviors of type 329J1 two-phase stainless steel have been examined by various methods of tensile, fatigue and creep rupture tests in the temperature range of room temperature to 1073K.
The results obtained are summarized as follows:
(1) The short time tensile strength of 329J1 two-phase stainless steel was higher than that of type 304 stainless steel at temperatures below about 850K. The serration appeared in the stress-strain curves obtained in the temperature range of 500 to 750K, accompanied with an increase in tensile strength. The appearance of such a serration is considered to be due to the dynamic strain aging caused by nitrogen.
(2) The flow stress of the α-phase was much higher than of the γ-phase at low temperatures, but at higher temperatures about 823K, it became lower than of the γ-phase. This result indicates that the strength of the two-phase stainless steel is influenced mainly by the α-phase at lower temperatures below about 823K and by the γ-phase at higher temperatures.
(3) The rotating bending fatigue strength and the fatigue ratio of type 329J1 steel were much higher than those of type 304 steel at all the testing temperatures. These high strength seem to be due to the phase separation of α-phase and α'or the precipitation of σ-phase.
(4) The appearance of“knee”in the S-N curve which is related with the coaxing effect, was recognized in the two-phase stainless steel. The reason for the appearance of such an effect is considered to be mainly due to nitrogen.
(5) The two-phase stainless steel exhibited a high creep rupture strength in spite of the existance of the α-phase which possesses a low strength at higher temperature. On the other hand, the creep rupture elongation was extremely large, for example, more than 150% at 1003K and the remarkable structural change was observed in the ruptured steel.
